docs/source/_static/scss/includes/_header.scss

.header {
    height: $header-height;
    background-color: $header-bg;
    display: flex;
    align-items: center;
    box-shadow: 0 0 10px rgba($black, 0.1);
    width: 100%;
    z-index: $z-index-header;
    flex-shrink: 0;
    display: flex;
    align-items: center;

    @extend %content-padding;
}

.logo {
    flex-shrink: 0;
    display: inline-flex;

    & > img {
        height: $logo-height;
    }
}

.nav {
    margin-left: auto;

    & > a {
        &, &:hover {
            color: $nav-color;
        }

        font-size: 0.95rem;
        line-height: 100%;
        padding: 0.4rem 1.2rem 0.55rem;
        border-radius: $border-radius-sm;

        &:not(:last-child) {
            & > span {
                position: relative;
    
                &::after {
                    content: '';
                    height: 1px;
                    width: 100%;
                    background-color: $nav-border-color;
                    bottom: -10px;
                    transform: translateY(0);
                    left: 0;
                    position: absolute;
                    opacity: 0;
                    transition: opacity 250ms, transform 250ms;
                    pointer-events: none;
                }
            }
    
            &.active,
            &:hover {
                & > span {
                    &::after {
                        transform: translateY(-4px);
                        opacity: 1;
                    }
                }
            }
        }

        &:last-child {
            border: 1px solid $theme-red;
            transition: background-color 300ms, color 300ms;

            &:hover {
                background-color: $theme-red;
                color: $white;
            }
        }
    }
}

.sidebar-toggle {
    position: relative;
    width: 40px;
    height: 40px;
    margin: 0 1rem 0 -0.35rem;
    cursor: pointer;
    border-radius: $border-radius-sm;
    transition: background-color 300ms;
    flex-shrink: 0;

    @include breakpoint-min(breakpoints(lg)) {
        display: none;
    }

    &:hover {
        background-color: $sidebar-toggle-hover-bg;
    }

    &::before,
    &::after {
        content: '';
        width: 100%;
        height: 100%;
        position: absolute;
        left: 0;
        top: 0;
        z-index: 1;
        background-position: center;
        background-repeat: no-repeat;
        opacity: 1;
        transition: opacity 250ms, transform 250ms;
    }

    &::before {
        background-image: $sidebar-toggle-icon;
        opacity: 1;
        transform: scale(1);
        
    }

    &::after {
        background-image: $sidebar-toggle-collapse-icon;
        opacity: 0;
        transform: scale(0.25);
    }
}

.sidebar-toggled {
    .sidebar-toggle {
        &::before {
            opacity: 0;
            transform: scale(0.25);
            
        }
    
        &::after {
            opacity: 1;
            transform: scale(1);
        }
    }
}